It was a great relief to Tom, to find that there was no danger from an earth tremor. Now that he had made up his mind to go in search of the diamond makers, he wanted nothing to interfere with it. Lest the feelings of Mr. Parker might be hurt by the mistake he had made, the young inventor cautioned Eradicate not to say anything more about the matter.

"'Deed an' I won't," he promised. "I'se only too glad dere wa'n't no earthquake, dat's what I am."

As for Mr. Parker, he did not appear much put out by his error in predicting.

"I am sure that what I heard was a tremor, due to some distant earthquake shock," he said. "The mule's kicking was only a coincidence."

And Tom let him have his way about it. The week was drawing to a close, and the Red Cloud was nearly in shape for the voyage. At almost the last minute Tom found that he needed some electrical apparatus for the airship, and as he had to go to Chester for it, he decided he would make the trip in his monoplane, and, while in the city, would also get the diamond pin he was having made for Mary Nestor.

He started off early one morning, in the swift little craft Butterfly, and soon had reached Chester. The diamond brooch was ready for him.

"It is one of the most beautiful stones we have ever set," the diamond merchant told him. "Don't forget, if you find any more, Mr. Swift, to let us have a chance to bid on them."

"I may," Tom promised, rather indefinitely. Then, having purchased his electrical supplies, he made a quick trip to Shopton, stopping on the way to call on Miss Nestor.

"Why Tom, I'm delighted to see you!" cried the girl, blushing prettily. "Did you come for some apple turnovers?" and she laughed, as she referred to a call Tom had once paid, when a new cook had been engaged, and when the pastry formed a feature of the meal.

"No turnovers this time," said the young inventor. "I came to wish you many happy returns of the day."

"Oh, you remembered my birthday! How nice of you!"

"And here is something else," added our hero, rather awkwardly, as he handed her the diamond pin.

"Oh, Tom! This for me! Oh, it's too lovely—it's far too much!"

"It isn't half enough!" he declared, warmly. "Oh, what a large diamond!" Mary cried as she saw the sparkling stone. "I never saw one so large and beautiful!"

"It's just as easy to make them large as small," explained Tom.

"Make them?" she looked the surprise she felt.

"Yes, I'm about to start for the place where diamonds are made."

"Oh, Tom! But isn't it dangerous? I mean won't you have to go to some far country—like Africa—to get to where diamonds are made?"

"Well, we are going on quite a trip, but not as far as that. And as for the danger—well, we'll have to take what comes," and he told her something of the proposed quest.

"Oh, it sounds—sounds scary!" Mary exclaimed, when she had heard of Mr. Jenks' experience. Do be careful, Tom!"

"I will," he promised, and, somehow he was glad that she had cautioned him thus—and in such tones as she had used. For Mary Nestor was a girl that any young chap would have been glad to have manifest an interest in him.

"Well, I guess I'll have to say good-by," spoke Tom, at length. "We expect to start in a couple of days, and I may not get another chance to see you."

"Oh, I—I hope you come back safely," faltered Mary, and then she held out her hand, and Tom—well, it's none of our affair what Tom did after that, except to say that he hurried out, fairly jumped into his monoplane, and completed the trip home.

As the Red Cloud has been fully described in the volume entitled "Tom Swift and His Airship," we will not go into details about it now. Sufficient to say that it was a combination of a biplane and dirigible balloon. It could be used either as one or the other, and the gas-bag feature was of value when the wind was too great to allow the use of the planes, or when the motive power, for some reason stopped. In that event the airship could remain suspended far above the clouds if necessary. There was provision for manufacturing the gas on board.

The Red Cloud was fitted up to accommodate about ten persons, though it was seldom that this number was carried. Two persons could successfully operate the machinery. There were sleeping berths, and in the main cabin a sitting-room, a dining-room, and a kitchen. There was also the motor compartment, and a steering tower, from which the engines could be controlled.

It was in this craft that the seekers after the diamond makers proposed undertaking the trip. Mr. Damon came on from his home in Waterfield about two days before the date set to leave, and Mr. Jenks, had, three days before this, taken up his abode at the Swift home. Mr. Parker, as has been stated, was already there, and he had put in his time making a number of scientific observations, though he had made no more predictions.

Nothing more had been seen of the mysterious man who had warned Tom, and the young inventor and Mr. Jenks began to hope that they had thrown their enemies off the track.

"Though I don't imagine they'll give up altogether," said Mr. Jenks.

"They're too desperate for that. We'll have trouble with them yet."

"Well, it can't be helped," decided Tom. "We'll try and be ready for it, when it comes," and then, dismissing the matter from his mind, he busied himself about the airship.

The food and supplies had all been put aboard, and they expected to start the next morning. In order to make sure that any stones which they might succeed in getting from the diamond makers were real gems, a set of testing apparatus was taken along. Mr. Parker had had some experience in this line, and, in spite of the fact that he might make direful predictions, Tom was rather glad, after all, that the scientist was going to accompany them.

"But what is worrying me," said Mr. Damon, "is what we are going to do after we get to Phantom Mountain. What are your plans, Mr. Jenks? Will you go in, and demand your share of the diamond-making business?"

"I have a right to it, as I invested a large sum in it, and I am entitled to more than a half-share. But, of course, I can't say what I'll do until I get there. We may have to act very secretly."

"I'm inclined to think we will," said Tom. "My plan would be to gain access to the cave, if possible, and watch them at work. We might be able to discover the secret of making diamonds, and, after all, that's what you want, isn't it, Mr. Jenks?"

"Yes, I paid my money for the secret, and I ought to have it. If I can get it quietly, so much the better. If not, I'll fight for my rights!" and he looked very determined.

"Bless my powder horn!" cried Mr. Damon. "That's the way to talk! And so we're to go cruising about in the air, looking for a mountain shaped like a man's head."

"That's it," a greed Mr. Jenks, "and when we find it we will be near Phantom Mountain, and the diamond makers."

The final details were completed that night. The last of the supplies had been put aboard, the larder was well stocked, the diamond testing apparatus was stored safely away, and all that remained was for the adventurers to board the Red Cloud in the morning, and soar away.

That night Tom was uneasy. Several times he got up, and looked toward the shed where the airship was stored. He could not rid himself of the idea that the men to whose interest it was that the diamond-making secret remain undiscovered, might attempt to wreck the airship before the start. Consequently both Eradicate Sampson and Engineer Jackson were on guard. Tom looked from his window, to the shed where the Red Cloud was housed. He saw nothing to cause him any uneasiness.

"I guess I'm just nervous," he mused. "But, all the same, I'll be glad when we've started."

They were all up early the next morning, Mr. Damon beginning the day by blessing the sunrise, and many other things that struck his fancy. The airship was wheeled out of the shed, and Tom gave her a final inspection.

"It's all right," he declared. "All aboard!"

"Now, do be careful," begged Mr. Swift. "Don't take too many chances, Tom."

"I'll not."

The adventurers were in the forward part of the ship, and Tom had taken his place at the wheels and levers in the pilot house. As he was about to start the motor he looked toward the road, and saw a horse and carriage. In the vehicle was a girlish figure, at the sight of which Tom blushed and smiled. He waved his hand.

"I came to wish you good luck!" cried Mary Nestor, for it was she in the carriage.

"Thanks!" cried Tom, leaning from the window of the pilot house. "It was good of you to get up so early."

"Oh. I'm always up early," she informed him.

"Look out that the motor doesn't scare your horse," Tom warned her.

"Old Dobbin doesn't mind anything," was her answer. "I'll see that he doesn't run away with me, as long as you're not on earth to rescue me. Good-by, Tom!"

"Good-by!" he called, and then he pulled the lever that set in motion the motor, and whirled the great propellers about. They whizzed around with a roar, and the Red Cloud, shivering and trembling with the vibration, rose in the air like some great bird.

"We're off for the West and Phantom Mountain!" called Tom to his companions.As the airship soared upward, Eradicate Sampson ran forward from where he had been standing near his mule Boomerang. He waved his hands, and shouted something.

"Bless my hatband! What does he want?" asked Mr. Damon, watching him curiously.

"It sounds as if he were calling to us to come back," spoke Mr. Parker.

"It's too late now," decided Tom. "Maybe he forgot to tell us good-by," but, he felt a vague wonder at Eradicate's odd motions; for the man was pointing toward the stern of the airship, as if there was something wrong there. But the Red Cloud soared on.